Method for the reduction of color variation in space-dyed yarn

ABSTRACT

A method for reducing variation in depth of shade, intensity and hue in space-dyed yarn comprises: injecting at least two liquid dye compositions into selected portions of a package of yarn to produce a yarn having different colors along the length of said yarn, preheating said yarn to a temperature of about 120°-200° F. using microwaves or radiofrequency, and heating said yarn to a temperature sufficient to fix said dye on said yarn.

FIELD OF THE INVENTION

[0001] The present invention relates to a method of preparing space-dyed or variegated yarn in which unwanted variations in depth of shade, intensity and hue are minimized. More specifically, the invention relates to such a method wherein dyed yarn is subjected to a preheating step using microwave or radiofrequency heat prior to heating the yarn (e.g., with steam) to a temperature sufficient to fix the dye.

BACKGROUND OF THE INVENTION

[0002] Space-dyed, or random dyed, yarn is yarn which is dyed different colors at various places along the yarn strand to produce segments of different colors along the length of the yarn. Woven, knitted or tufted fabrics produced from space-dyed yarn have “flecks” and/or pools of different colors at variable portions of the finished fabric, adding variety and style to an otherwise plain fabric.

[0003] One of the methods used to produce a space-dyed yarn is known as the “package space-dyed” method. This method involves taking a wound package of yarn and applying different colors to different quadrants or sections of the package and is described, for example, in U.S. Pat. No. 3,120,422. The patent teaches applying the colors by injecting needles into the package either from above and below the package or laterally, and then pumping the colored liquor, comprising selected dyes and auxiliary chemicals, acids, wetters and alkalis, as required, into the package. Once the package has the desired amount of color injected, the package can be hydro-extracted, or spun, to remove moisture down to 60-100% of the yarn weight. Under these conditions, the liquid will not migrate rapidly to the bottom of the package if it sits for a period of time prior to the step of fixing the dye to the yarn. Another method of applying color employs using a vacuum on the package, inducing the dye liquor to penetrate where the air has been removed.

[0004] Once the color has been applied, the dyestuff must be fixed to the fiber. The method used for this process varies depending on the fiber type. Wool, acrylic and nylon fibers ordinarily require that the yarn package be heated to about 200-220° F. for about 5-20 minutes, and polyester fibers require the package to be heated to about 265-275° F. for about 20-60 minutes.

[0005] The currently accepted and practiced method for heating the packages is to place them in an enclosed steam chamber (e.g., an autoclave) and then inject steam into the container under pressure. The steam slowly permeates the package and heats the yarn. Most autoclaves can utilize a vacuum step which removes air from the container and the yarn package, thus allowing the steam to more quickly and completely penetrate the yarn package.

[0006] Unfortunately, this method of heating dye packages with steam produces an undesirable variation in depth of shade, intensity and hue between the yarn at the extreme outside of the package and the yarn at the inside of the yarn mass of the package. Steam enters the package from all exposed surfaces, and as it moves into the package some condensation occurs. This condensation, and the general movement of the steam, causes dye color and particles to migrate through the yarn, generally toward the center of the yarn mass. At the same time, the steam entering the package has the tendency to wash off or dilute the dye color at the extremities of the yarn package. The resulting product has lighter portions of color on all exposed surfaces of the package.

[0007] To date, the industry has handled this problem by “stripping” the lighter yarn from the outside of the package and wasting it, then winding the entire package onto another tube and “stripping” still more yarn from what had been the inside extremity on the original tube and wasting it. This second step is necessary because the tubes on which yarn is wound prior to the injection of the dyes typically are perforated, resulting in steam ingress through the perforations of the tube such that the yarn wound close to the tube also is lighter in color than the yarn at the center of the yarn mass.

[0008] Even after “stripping” and wasting this yarn, however, there still is significant variation in depth of shade, intensity and hue from the inside to the center to the outside of the package. Consumers have used various procedures to try to minimize in their final product the undesirable effects of the variations in yarn dyed using these conventional techniques through various weaving, knitting, tufting and handling techniques. In some cases, consumers co-mingle or ply the space-dyed yarn with other yarns, including other space-dyed yarns, to minimize the undesirable effects of the variation in the space-dyed yarn.

[0009] Polyester fiber appears to be the most sensitive fiber for this color variation problem, as the dyes do not form a true solution and are in dispersed form. This means that they can migrate easily in the yarn packages.

[0010] In view of these problems in achieving even dyeing of the yarn, improvements in the process for dyeing and fixing space-dyed yarns are sought.

SUMMARY OF THE INVENTION

[0011] Accordingly, the process of this invention comprises a method for space dyeing yarn which comprises:

[0012] a) injecting two or more liquid dye composition into selected portions of a wound package of yarn to provide a yarn having different colors along the length of the yarn;

[0013] b) preheating said yarn to a temperature of about 120°-200° F. using microwave or radiofrequency heat; and

[0014] c) heating said yarn to a temperature sufficient to complete fixation of said dye on said yarn.

[0015] Typically, this latter heating step is carried out at a temperature of about 260°-275° F. for polyester yarn and at a temperature of about 200°-220° F. for nylon, wool and acrylic. For all of these yarn types, the heating step can be carried out in a steam chamber under pressure, such as an autoclave. Alternatively, wool, acrylic and nylon dye fixation can be accomplished by leaving the yarn in the microwave or radiofrequency heater used for the preheating step, and heating the yarn at a temperature within the range of about 200°-212° F. for a time sufficient to fix the dye, typically about 10-20 minutes.

BRIEF DESCRIPTION OF THE FIGURE

[0016]FIG. 1 is a graph showing color variations in yarn dyed and fixed according to a conventional procedure and yarn dyed and fixed in accordance with the method of this invention.

DETAILED DESCRIPTION OF THE INVENTION

[0017] It now has been found that variations in color or depth of shade of a space dyed yarn can be minimized or eliminated by subjecting the dyed yarn to a microwave or radiofrequency pre-heating step prior to heating the yarn to fix the dye.

[0018] In accordance with this invention, wound packages of yarn are space-dyed in accordance with any accepted method. Most common is the dye injection procedure described above. Typically, between two and about six different colors are injected into the yarn. Once as many colors as desired have been injected into the wound yarn and the wet yarn has been hydro extracted to remove moisture to about 60-150%, the yarn package is preheated to a temperature within the range of about 120°-200° F. by subjecting the yarn to microwave radiation or radiofrequency heat. Preferably, if the yarn is an acrylic, nylon or wool yarn, the yarn is heated to a temperature within the range of about 180°-200° F.; if the yarn is a polyester yarn, it preferably is heated to a temperature within the range of about 120°-180° F. In each instance, the yarn preferably is held at the desired temperature for about five minutes.

[0019] Once the yarn has been preheated, the yarn package is removed promptly from the chamber in which the preheating step occurred and placed in a steam heat enclosure, such as an autoclave. Steam is introduced to the enclosure in accordance with conventional techniques and applied for a period of time sufficient to fix the dye to the yarn. The temperature within the enclosed chamber typically is within the range of about 200-275° F., depending upon the type of yarn. For polyester yarn, the temperature in the steam chamber desirably is brought to within the range of about 265°-275°F; for nylon, wool and acrylic yarn, the temperature only needs to be raised to be within the range of about 200°-220°F.

[0020] The timing of the transfer from the preheating chamber to the steam heat enclosure is such that the package should be at room temperature for a minimum of time, desirably no more than about 20 minutes. Otherwise, the outer surface of the yarn package can cool sufficiently that the benefits of the pre-heating step begin to deteriorate.

[0021] As an alternative to fixing the dye in a steam chamber, for wool, acrylic and nylon yarns, the dye can be fixed before the yarn is removed from the microwave or radiofrequency heater. The heating temperature is increased to be within the range of about 200°-212° F. and the yarn is maintained at this temperature for about 10-20 minutes.

[0022] By subjecting the dyed yarn to this microwave or radiofrequency preheating step, the variations in depth of shade, intensity and hue that typically occur during conventional fixing steps has been found to be negligible. The dyes can be fixed without causing any migration of color towards the center of the yarn package.

[0023] Either microwave radiation or radiofrequency heating can be used in the method of this invention. One advantage of radiofrequency heating is that it acts only on water and does not heat or shrink plastic tubes on which yarn conventionally is wound. Radiofrequency heating can be carried out in a number of commercially available machines. For example, Strayfield Fastran makes several models of RF dryers which can be modified for use as a heating unit. One suitable unit, for example, is the FASTRAN PAG60. Since such units primarily are used for drying, some modifications must be made. The airflow across the packages must be eliminated to reduce drying. Without such modification, the drying will cause dispersed dyes to migrate to the outside of the package, producing a very dark “skin” on the package. This can be corrected by placing the packages in an enclosed Plexiglass “coffin” with a lid to retain the moist air created when the packages are heated, and to protect the packages from the cooling fans which keep the generator cool.

[0024] The model PAG60 has a 60 kW generator. A full load of 50 two-pound packages of yarn at 60% wet pickup takes about 4 minutes to reach 160 F. The evenness of heating is an important factor, as all packages must be within 10° F. of one another to obtain the desired benefits of the method of the invention. This can be checked by means of an infrared thermometer device. The unit controls must be modified to provide energy until a fixed temperature is reached.

[0025] If the pre-heating step is carried out in a microwave, conventional, commercially available microwave units can be employed. For microwaves with 1000 kW, it takes about 7½ minutes for a two-pound package of yarn to reach the desired temperature.

[0026] Dyes which can be used in accordance with the present method include those conventionally used for the dyeing of nylon, acrylic, wool and polyester yarn. For polyester, such dyes include:

[0027] a) high energy dispersed dyes for the automotive polyester industry, such as:

[0028] Dispersed Yellow 42

[0029] Dispersed Yellow 86

[0030] Dispersed Orange 41

[0031] Dispersed Orange 30

[0032] Dispersed Red 86

[0033] Dispersed Red 167

[0034] Dispersed Red 191

[0035] Dispersed Blue 77

[0036] Dispersed Blue 60

[0037] b) many mixes of dispersed dyes, such as:

[0038] Dorosperse Dk Red KGL

[0039] Dorosperse Red KRR

[0040] c) dyes without listed color index numbers, including:

[0041] Dianix Yellow HF-4G

[0042] Dianix Red HF-g

[0043] Dianix Red HF-B

[0044] Dianix Blue HF-2G

[0045] Terasil Blue HLB

[0046] Terasil Red HL-R

[0047] Terasil Yellow HL-G

[0048] Terasil Yellow GWL

[0049] Terasil Pink 2GLA

[0050] Preferred polyester dyes include:

[0051] Terasil Yellow GWL

[0052] Terasil Blue HLB

[0053] Terasil Pink 2GLA.

[0054] For nylon and wool, useful dyes include acid and premetalized dyes, such as:

[0055] Acid Yellow 169

[0056] Acid Orange 156

[0057] Acid Red 336

[0058] Acid Blue 324

[0059] Acid Black 194

[0060] Acid Yellow 49

[0061] Acid Red 337

[0062] Acid Yellow 151

[0063] Acid Black 60

[0064] Acid Red 182

[0065] Preferred dyes for nylon include: Acid Yellow 169 (Nylanthrene Orange 3G) Acid Red 336/mix (Telon Red 2BN) Acid Blue 324 (Nylosan Blue EC/BGL)

[0066] Preferred dyes for wool include: Acid Yellow 151 (Isolan Yellow NW) Acid Black 60 (Intralan Gray BL) Acid Red 182 (Irgalan Red BL)

[0067] Suitable dyes for use on acrylics include:

[0068] Basic Yellow 28

[0069] Basic Red 46

[0070] Basic Blue 41

[0071] Basic Blue 3

[0072] Basic Red 46

[0073] Basic Red 14

[0074] Basic Violet 16

[0075] Basic Green 4

[0076] Preferred dyes for use on acrylics include: Basic Yellow 28 (Astrazon Gold Yellow GL) Basic Red 46 (Astrazon Red FBL) Basic Blue 41 (Astrazon Blue FGGL)

[0077] Each of these dyes, and other commercially available dyes, can be used in the preparation of conventional dyeing compositions. For example, dye compositions for polyester typically can include a dispersed dye in combination with at least one dispersant, antimigrant, pH buffer, and/or wetter. Dye compositions for wool and nylon typically comprise an acid or pre-metallized acid dye in combination with at least one wetter or pH control agent, and dye compositions for acrylic yarns typically can comprise a basic dye in combination with at least one retardant, pH control agent, or wetter. The choice of acceptable auxiliary components to be combined with a dye and the preparation of specific suitable dye compositions is well-known to persons of ordinary skill in the art. Accordingly, in accordance with the present invention, space-dyed nylon, wool or acrylic yarn is subjected to a pre-heating step wherein the yarn is heated by microwaves or radiofrequency to a temperature of about 120-200° F., preferably about 180-200° F., usually for a period of about 5 minutes, then the preheated yarn is heated to a temperature of about 200-220° F. to completely fix the dye, either by subjecting the yarn to steam heat in an enclosed steam chamber or by increasing the temperature in the microwave or radiofrequency heater. Also in accordance with this invention, dyed polyester yarn is subjected to a pre-heating step wherein the yarn is heated by microwaves or radiofrequency to a temperature of about 120°-200° F., preferably about 180°-200° F., generally for a period of about 5 minutes, then the preheated yarn is heated to a temperature of about 265-275° F. by subjecting the preheated yarn to steam heat in an enclosed steam chamber for a period of time sufficient to fix the dyes.

[0078] In each instance, the resulting dyed yarn is characterized by colors which retain their hue and color depth throughout the length of the yarn.

[0079] The present invention will be further illustrated by the following example, which is not to be construed as limiting.

EXAMPLE

[0080] In order to demonstrate the process a solid shade was selected rather than a multicolor, as the solid shade can be read quantifiably on the color spectrophotometer, while it is not possible to accurately read multicolored fabrics.

[0081] Two samples of approximately two pounds each of 1/150 automotive quality polyester yarn were wound onto 3 inch diameter perforated plastic dye tubes.

[0082] One tank of 50 liters of dye was mixed using the following formula: 2 g/l Amwet DJW Non-ionic Wetter 0.5 g/l Amwet DOSS DOSS 8.0 g/l Pomoco SN-2 Snythetic Antimigrant 10 g/l Pomasperse IL Dispersant 10 g/l Buffer 5 pH Buffer 1.31 g/l Terasil yellow GWL 0.613 g/l Dorosperse Dk Red KGL 1.416 g/l Terasil Blue HLB

[0083] The dye was injected into both packages at 250% wet pickup, using a multiple needle injection unit, with a number of needles upper, and a number of needles lower.

[0084] Following injection, the packages of yarn were extracted to 60% wet pickup by spinning for 12 seconds in the centrifuge.

[0085] One package was placed in a FASTRAN PA60 radio-frequency heater, together with 49 other packages of undyed polyester, each with an equivalent moisture content, to ensure that the machine operated with a full load.

[0086] With the RF energy setting at 75%, the unit was activated and the yarn heated for four minutes. Upon exit, the temperature was measured and was 160° F. on the outside of the package.

[0087] Both packages were then placed on an autoclave trolley, and placed in the autoclave. A cycle was run where the temperature was increased to 275° F. and held there for 60 minutes.

[0088] Both packages were removed, reduction cleared, and rinsed. After drying, a complete sock was knitted of each yarn package.

[0089]FIG. 1 below is a graph on which has been plotted the color difference along the yarn, once it has been knitted into a sock (done for purposes of ease of reading the color). Readings were taken at six foot intervals along the sock, and the total number of readings represents the total color cross section from the very inside to the outside of the package. The graph plots the color difference in DE color units. The standard or reference color was the color in the center of the package (or sock). As can be seen, the color variation is significantly improved, resulting in color variation within a single space-dyed package which is significantly smaller than in the control. 

1. A method for space dyeing yarn which comprises injecting two or more liquid dye compositions into selected portions of a wound package of yarn to produce a yarn having different colors along the length of said yarn, preheating said yarn to a temperature of about 120°-200° F. by subjecting said yarn to microwave or radiofrequency heating, and heating said preheated yarn at a temperature and for a time sufficient to fix said dye on said yarn.
 2. A method according to claim 1, wherein the yarn comprises polyester, nylon, acrylic, or wool.
 3. A method according to claim 1, wherein said yarn is preheated using microwave heating.
 4. A method according to claim 1, wherein said yarn is preheated using radiofrequency heating.
 5. A method according to claim 1, wherein said preheated yarn is heated with steam to fix said dye.
 6. A method according to claim 5, wherein said steam heat heats said yarn to a temperature of between about 200°-275° F.
 7. A method according to claim 2, wherein said yarn comprises polyester yarn and is subjected to microwave or radiofrequency heating to a temperature of about 120°-180° F. and subsequently subjected to steam heat at a temperature of about 265°-275° F. for a period of time sufficient to fix said dye on said yarn.
 8. A method according to claim 2, wherein said yarn comprises acrylic, nylon or wool and is subjected to microwave or radiofrequency heating to a temperature of about 180°-200° F. and subsequently subjected to steam heat at a temperature of about 200°-220° F. for a period of time sufficient to fix said dye on said yarn.
 9. A method according to claim 1, wherein said yarn comprises polyester and said dye composition comprises a dispersed dye.
 10. A method according to claim 9, wherein said dye composition further comprises at least one dispersant, antimigrant, pH buffer, or wetter to promote dye fixation on said yarn.
 11. A method according to claim 1, wherein said yarn comprises wool or nylon and said dye composition comprises an acid or pre-metallized acid dye.
 12. A method according to claim 11, wherein said dye composition further comprises at least one wetter or pH control agent to promote dye fixation on said yarn.
 13. A method according to claim 1, wherein said yarn comprises an acrylic and said dye composition comprises a basic dye.
 14. A method according to claim 13, wherein said dye composition further comprises at least one retardant, pH control agent or wetter to promote dye fixation on said acrylic yarn.
 15. A method according to claim 1, wherein said yarn is an acrylic, wool or nylon yarn and said preheated yarn is heated in said microwave or radiofrequency heater to fix said dye on said yarn.
 16. A method according to claim 15, wherein said preheated yarn is heated to a temperature of about 200°-212° F. to fix said dye to said yarn. 